Myron Strongin

a‐Si : H produced by high‐temperature thermal decomposition of silane

Hydrogenated amorphous silicon has been deposited by a new technique of thermal decomposition of silane from a hot tungsten or carbon foil heated to about 1600 °C. Initial measurements indicate that the resulting films have a fairly high photoresponse. Introduction of ammonia along with silane is seen to enhance the photoconductivity quite significantly.

The interaction of oxygen and nitrogen with the niobium (100) surface: II. Reaction kinetics☆

Abstract Auger spectroscopy has been used to investigate the interactions of oxygen and nitrogen with both the (100) face niobium and with polycrystalline niobium. Sticking coefficients for both gases have been determined as a function of coverage. A temperature and concentration ependent segregation of oxygen at the surface has been observed even under conditions where the solid solubility of the bulk was not exceeded. A model to describe this segregation has been developed and extended to explain discrepancies in earlier investigations f the reaction of oxygen with niobium.

The interaction of oxygen and nitrogen with the niobium (100) surface: I. Morphology☆

Abstract Low energy electron diffraction has been used to investigate the reactions between nitrogen and oxygen and the (100) face of niobium. Several different oxygen containing surface structures were observed.

Surface segregation of oxygen in NbO and Ta alloys

Abstract Large amounts of oxygen segregate to surfaces of niobium and tantalum even though the bulk oxygen concentrations are extremely small. Studies made on alloys containing 0.1 atom percent and higher bulk oxygen indicates that the segregation is localized to the 5–15rA region near the surface. Oxygen redistributes back and forth between bulk and surface reversibly as a function of temperature and equilibrium is established almost instantaneously above about 825°C. Desorption of oxygen, probably in the form of oxides (1, 2, 7), became appreciable beyond 1200°C. In the intermediate temperature range the surface reached a steady equilibrium state, from which the distribution coefficient could be obtained. In this temperature range, ΔH for oxygen segregation varied from 17 to 11 kcal/g·atom in niobium and 19 to 6.6 kcal/g·atom in tantalum as the bulk oxygen varied from 0.1 to 2 atom percent.

The superconducting transition temperatures of disordered Nb, W, and Mo films☆

Abstract Large changes in T c are observed in films of Nb, W and Mo evaporated under ultrahigh vacuum conditions onto cryogenic substrates. An explanation of these temperature changes in terms of the smearing of N (0) due to the small mean free path is discussed.

Oxidation of {100} and {111} surfaces of pyrite: Effects of preparation method

Abstract Photoelectron spectroscopy was used to investigate the surface structure and reactivity of two pyrite {100} surfaces, prepared by different means. Specifically, synchrotron-based S 2p photoemission data for a {100} pyrite growth surface prepared by exposure to HCl, and one resulting from mechanical fracture suggested that the acid-washed growth surface showed a higher concentration of elemental sulfur and/or polysulfide impurities. The surfaces, however, showed a similar initial oxidation reactivity under a well-controlled H2O/O2 gaseous environment, implying that the fraction of both surfaces that underwent the initial oxidation reaction were similar in structure. The amount of initial oxidation on these surfaces, however, was significantly lower than on an acidwashed {111} growth surface. Photoelectron and ion scattering spectroscopy offer some possible reasons for this structure sensitivity.

Charge density wave formation accompanying ferromagnetic ordering in quasi-one-dimensional BaIrO3

The magnetic, transport, optical, and structural properties of quasi-one-dimensional BaIrO 3 show evidence for the simultaneous onset of electronic density wave formation and ferromagnetism at Tc3a 175 K: Two additional features in the chain direction dc conductivity show a sudden change to metallic behavior below Tc2a 80 K and then a Mott-like transition at Tc1a 26 K: Highly non-linear dc conductivity, optical gap formation at <9kBTc3, additional phonon modes, and emergent X-ray satellite structure support density wave formation. Even at very high (30 T) fields the saturation Ir moment is very small, <0.04mB/Ir. q 2000 Elsevier Science Ltd. All rights reserved.

Uptake rates for hydrogen by niobium and tantalum: effect of thin metallic overlayers☆

Abstract The hydrogen uptake rates of clean niobium and tantalum foils were measured as a function of temperature and pressure. The “sticking coefficient” (the number of hydrogen atoms entering the bulk per twice the number of hydrogen molecules hitting the surface) of hydrogen on clean niobium and tantalum at about 2.2 × 10−5 Torr hydrogen and room temperature was found to be surprisingly low, approximately 0.005 and 0.05 respectively, resulting in very low uptake rates under these conditions. This result is explained on the basis of a recently proposed model. It was found that these uptake rates can be significantly enhanced or decreased by the surface deposition of a thin layer of palladium, platinum or nickel. The hydrogen uptake rates, i.e. the sticking coefficients, were measured as a function of the overlayer thickness. In the case of palladium it was found that a layer less than one monolayer thick either will not change or will even inhibit the hydrogen uptake, whereas a layer over one monolayer thick will dramatically enhance the sticking coefficient to a value of unity. It was found that the change at one monolayer is related to a phase transition of the palladium surface layer at that coverage. Neither platinum nor nickel exhibits this effect but both influence the uptake rate by an amount depending on their thicknesses. Thick overlayers of platinum, nickel and palladium inhibit uptake because of a limited permeation rate through the layer.

Infrared Studies of the Onset of Conductivity in Ultrathin Pb Films

In this paper we report the first experimental measurement of the low-temperature, normal-state infrared conductivity of ultrathin quenched-condensed Pb films. For dc sheet resistances such that vt o 1 the ac conductance increases with frequency but is in disagreement with the predictions of weak localization. We attribute this behavior to the effects of an inhomogeneous granular structure in these films when they are first formed, which is manifested at the very small probing scale of infrared measurements. Our data are consistent with predictions of two-dimensional percolation theory.

Formation and growth mechanism of B10N nanotubes via a carbon nanotube–substitution reaction

A substitution-reaction route has been demonstrated as an efficient synthesis route for producing single-walled and multiwalled B10N nanotubes (BNNTs). The nanotubes have diameters smaller than those of the starting carbon nanotubes and also have similar lengths to the starting carbon nanotubes. The isotopic ratio of B10 in BNNTs depends on the isotopic ratio of the starting B2O3. A detailed growth model is also given for the carbon nanotube–substitution reaction.